Local area networks (LANs) have come into widespread use in industry and business. The token ring network has become one of the most popular forms of LAN, owing to its implementation by the International Business Machines Corporation (IBM). Moreover, the standards for token ring networks are now well defined in IEEE standard 802.5 of the Institute of Electrical and Electronic Engineers and this standard has now been adopted as a draft International Standard ISO DIS 8802/5, so that a high degree of consistency and uniformity in token ring networks can now be expected.
In accordance with the IBM implementation, a nonintelligent, distributed concentrator, called a multi-station access unit (MAU) is utilized to provide access by stations to the token ring network. One of the major advantages of using MAUs is that they can be in a distributed configuration. That is, a MAU is therefore conveniently brought to a location, such as the location of a work group, and all of the users can be placed on the network by simply having their computers connected to the MAU through an appropriate cable. Internally, each MAU couples the connected stations in a series ring on a trunk cable, and individual MAUs can be connected in tandem through the trunk cable to form the overall network ring.
Although the use of distributed MAUs is a highly desirable and effective convenient network configuration the IBM implementation suffers from a number of shortcomings. First of all, it is only possible to connect all of the MAUs, and therefore all of the stations, in a single ring. As the number of stations grows, this results in access becoming increasingly more difficult and slower operation of the network. Token ring networks have been. available which provide multiple rings, but this has typically required sacrificing the distributed nature of the IBM implementation, with the resultant disadvantage that cables must be run from each station to a central location.
Another shortcoming of the IBM implementation the difficulty of determining the physical location of a station in the network. Although each station has a unique address, the system supervisor has no way of knowing the physical location of the station on the ring unless he keeps track of it himself when first installing new users. Furthermore, this could present a serious security problem, in that, should an unauthorized user connect his station to the network, it could be some time before the network supervisor could locate that user and physically disconnect him.
One recognized shortcoming of token ring networks is the difficulty of locating and isolating faulty stations. Fault detection procedures have been built into the operating protocol, but quick and efficient means for locating and isolating faults have not been available.
Broadly, it is an object of the present invention to provide a method and apparatus for configuring and maintaining token ring networks which avoid the shortcomings of existing methods and apparatus. It is specifically contemplated that the invention should not compromise the distributed nature of the IBM implementation of token ring net works.
It is another object of the invention to provide an apparatus for configuring token ring networks which will permit the use of distributed concentrators yet permit the selective assignment of individual stations to any one of a plurality of different, parallel communication rings of the network.
It is yet another object of the present invention to provide a method and apparatus for configuring and maintaining token ring networks which will automatically detect the address of a station connected to the network and associate that station's address with the station's physical location.
It is yet another object of the present invention to provide a method and apparatus for configuring and maintaining token ring networks which will permit rapid and convenient monitoring of the operational status of each station of the network.
It is also an object of the present invention to provide a method and apparatus for configuring and maintaining token ring networks which are convenient and reliable in use, yet relatively inexpensive to install and maintain.
In accordance with an illustrative embodiment demonstrating objects and features of the present invention, an enhanced MAU (EMAU) is provided which can be used in token ring networks in place of existing MAUs yet permits each station on the network to be selectively connected to any one of a plurality of different token ring trunk cables. The EMAU uses the conventional trunk coupling units (TCU) of an MAU, which permit a station to be connected in the ring or to be bypassed, but adds to each TCU a multi-switch device which permits the TCU to be connected to one of a plurality of ring trunk cables while providing a bypass across the station in the remaining ring trunk cables.
In addition, the EMAU provides sensing of the input and output signal for each station. This permits the EMAU to monitor the address produced by each station during the normal ring polling process which occurs during neighbor notification operation of the token ring network. It is then possible to associate each address with a physical location of a station, since the physical location is known. Sensing of the input and output signal is also utilized to perform a peak amplitude comparison between the two, to derive signals indicative of the input-output operability of each station.